Grimethorpe filter element performance—the final analysis

Abstract

A demonstration hot gas filter, funded by the Electric Power Research Institute and installed in a pressurised fluidised bed combustor at Grimethorpe, South Yorkshire, UK was operated for a second period in 1991–92 for the Grimethorpe Topping Cycle Project (GTCP). This project was aimed at assessing the feasibility of running a gas turbine on coal-derived gas as part of the development programme for the Air Blown Gasification Cycle (formerly known as the British Coal Topping Cycle).As in previous studies operation of the filter led to progressive changes to the mechanical properties of the tubular clay-bonded silicon carbide filter elements. In order to explain the mechanisms behind these changes and thus determine operating conditions which influence element properties and performance detailed element characterisation and microstructural studies have been carried out. It has been found that slow bond devitrification and the development of a bond-grit interlayer of cristobalite led to changes in the integrity of the interface, with loss of strength and elastic modulus and a decrease in ultrasonic pulse velocity through the material. Microstructural studies suggest that the combination of the upper temperature of operation (≈ 830°C) and the thermal cycling during reverse pulse cleaning to remove the dust cake results in microcracking. While the strength losses experienced did not result in in-plant element failures, the reliability of the elements would be improved if operation can be limited to a temperature at which devitrification of the element's bond material is minimised.